In general, an image sensor is a semiconductor device that converts an optical image into an electrical signal. The image sensors are generally classified into charge coupled devices (CCDs) and complementary metal oxide silicon (CMOS) image sensors (CISs).
The CIS includes a photodiode for sensing an irradiated light and a CMOS logic circuit for processing the sensed light into an electric signal for data. As the amount of light in the photodiode increases, the photosensitivity of the image sensor improves.
To increase the photosensitivity, one technique is to increase a fill factor (a ratio of a photodiode area to an entire area of the image sensor). Another is a technique in which the path of light incident into a region other than a photodiode is changed to focus the light on the photodiode.
A typical example of the focusing technology includes a microlens formation. In the microlens formation, a convex microlens is formed of an excellent light transmission material on the photodiode such that more incident light can be directed onto the photodiode region by refracting the incident light.
In this case, the light parallel to an optical axis of the microlens is refracted through the microlens, and thus the focus of the microlens is formed at a predetermined position of the optical axis.
Typically, a CIS is classified according to the number of the transistors in a pixel. For example, the CIS can be classified as a 3T, 4T, or 5T type. The 3T includes one photodiode and three transistors. The 4T includes one photodiode and four transistors.
Hereinafter, a related art CIS will be described with reference to FIG. 1.
FIG. 1 is a sectional view of the related art CIS.
As illustrated in FIG. 1, a photodiode 12, an interlayer insulation layer 13, and a color filter layer 14, and a planarization layer 15 are sequentially formed on a substrate 11. Then, a microlens 16 is formed on the planarization layer 15.
However, the related art CIS has following problems.
For example, as illustrated in FIG. 1, incident light in tilt, which is not parallel to an optical axis of the microlens, included in light incident into the color filter 14 through the microlens 16 is induced into the photodiode 12 of another pixel and not the photodiode corresponding to the color filter. Thus, crosstalk occurs such that light becomes mixed and light sensitivity decreases.